Community Forums

mel s · 11-09-2012, 02:29 PM

Quote:

Originally Posted by JimM68

Thank you. 12 is way out there still, but only somewhat questionable.
I'm still thinking a 300 mile run, fillup to fill up, flat ground, on highway mile markers, might be in order...
If it turns out to be real, you'll have a lot of us looking at trading our ISC's for 6.7 ISB's...
your rig is a 33k GVWR, right?

For now, I'll standby my previous statements that Class A motorhome, gas or diesel, get 7 mpg, more or less, that is, 6 to 8.

Over 25 years ago, I was told by a gentleman with years of, and multiple, RV ownership:
"If anyone tells you they consistently average over 9 MPG with a gas coach and over 10 with a diesel, THEY ARE LYING"!
I believe that is still the case.

I've also heard that figures don't lie but lairs sure can figure!

Mel Stuplich
'96 Safari Sahara, 8.5 MPG over 100k miles

Dutch Star Don · 11-09-2012, 02:32 PM

deSanford...... I know this post kind of got blown out of porportion because many didn't see your other post about the programmer/mileage issue. As Walt said, it needs to be calibrated, including the VMSpc, even though the program lets you select your exact engine. I initially tried to calibrate my VMSpc by looking at the mpg and making changes. I found it easier to look at the gallons used at each filliup. When you make a correction on the VMSpc, it changes your lifetime mpg, lifetime gallons used, recent mpg and recent gallons used (since last fillup). To get mine more accurate, I filled the coach and checked the gallons it took vs what the VMSpc said it used. It took me several fillups to get them so they were almost identical. I actually adjusted it so that it was calibrated to show that I used a little more than I took (maybe 3/10's 5/10's more on a 35 gallon fillup).

On the VMSpc, I could change the gallons used via a correction, before I erased the gallons used information since the last fillup. So if I took 35.3 gallons, I came in and checked what the VMSpc said. If it said I used 34.2, I could make a correction, hit the OK button and it would instantly change to a new gallons used number. I did this on several fillups and I think I'm as close as I can get. I also will drop a jack when fueling to make sure the coach is relatively level and taking the same amount of fuel each time.

For a while, before the minute corrections, I was seeing 10.3 from ISL (short/lite coach, not towing) on flat ground. As I dialed in the corrections, I'm now down to about 10 on a really perfect trip that has few hills, no wind and a lot of freeway driving.

The VMSpc has a lifetime mpg counter and still shows my liftime mpg is 8.5. I changed the engine fan and started driving slower about a year ago which has increased my mpg, but will not reflect on the lifetime mpg for a long time since I already had 45000 miles on my coach before the changes.

I hope this makes sense. For those with an ISL and the VMSpc, I have the correction number you need to make in the "Engine Corrections" field that will get your VMSpc to read your mpg fairly accurately or at least a good starting point.

deSanford · 11-09-2012, 06:03 PM

Mel can you read my posts? deSanford

deSanford · 11-10-2012, 08:20 AM

To re calibrate the TCM I sent it to Detroit Allison in Coburg, ORE. It cost $200.00 for Ron to bring the TCM to 55MPH in 6th gear overdrive. What a difference on MPG. deSanford

Barlow46 · 11-10-2012, 08:53 AM

deSanford...stick with me here as I have some concerns about what you are doing to get this significant MPG improvement. Before I try to explain my concern, what is the rear end gear ratio you have in your setup? The original setup in your coach was determined by engine output, gear ratio's and weight. For example, if I take my present boat and outboard engine and start changing props, I can either improve "hole shot", top speed, performance with max. weight, etc. However this may come at a cost. Suppose I want to improve just cruising range (mpg or gph), then I would just pick a prop that would put me on a plane at a lower rpm. This would work but it would be detrimental to the engine as the engine may not be operating in a range that keeps it from "lugging" so to speak. The engine will suffer in the long run as it is "overworking at a lower rpm" to keep the boat on a plane. There is actually more to this problem but in a nutshell, damage will be done to the engine. This is my concern with what you have setup with the TCM to 55mph in 6th gear. If the engine along with the transmission and gear ratio can handle this and stay within safe parameters, then you are fine but I am not seeing all of this happen with an engine with lower torque and HP. Have you had any discussion with the "experts" about this possibility?

Dutch Star Don · 11-10-2012, 01:07 PM

deSanford.....I'm glad Barlow46 brought this up. It's your coach and we all try different things for improved performance, but is what you're doing safe. In another post you stated that you're going to change out the Source Engine fan for a Horton. That didn't make snese to me because the Source gives you HP all the time when the Horton only gives it too you when it's cool. You replied by saying that you needed the cooling when climbing because, essentially, you were running really low RPM's.

Ever since your response on the other post about cooling:

"Yes Don I would be the first to use a Horton brand fan clutch on a ISB340 6.7L Cummins in the good ole USA. Climbing hills with the "modified chipped" engine in 6th gear at 55MPH my RPM is less then 1,500. The Source fan and the stock fan use about the same HP (at this RPM). Where the Source fan really shines is at a much higher RPM. That being said on long uphill climbs as you can imagine my water and transmission temps rise. That is why I'm going to go back to the stock fan. deSanford"

It didn't make sense as to why you would want to run low rpm's when climbing, especially if you're running hot. Diesels need that rpm increase when they get hot to get everything cooling better.

It's your coach and you may be trying some exotic things for mpg, but are you playing with fire? I never really responded to your above because I thought maybe I'm not comprehending what you're doing. Now that Barlow46 has brought it up, it's got me wondering again.

Not giving you a hard time, just trying to understand some things you're changing. Now if you're working on a secret formula for improved diesel mpg, I'll keep your secret, even provide some funding and will figure out how to split the profits!

SteveSkinner · 11-10-2012, 03:08 PM

I'm thinking 55 mph in 6 th gear is really a cruise setting.
It puts your Diesel engine in a good torque range and your foot is not hard down on the throttle.
A perfect situation for saving fuel.
As soon as you increase throttle setting it will downshift and you are back to the original spec.
I can only see a win win here.
My new Subaru 6 speed now cruises at 2800 rpm at 70 mph where the old did 3400.
I can't get much acceleration at 2800 rpm but it will cruise all day at substantially lower fuel consumption.

DeadRinger · 11-10-2012, 03:21 PM

So all MPG bashing aside and back to the primary reason for this post and the reason I came here, TCM programming. So I wanted to know more about TCM tuning and I can care less about the MPG or other issues.

deSanford what MPH does the trans shift into 6th gear? I know you said 55 but does it shift into 6th at 53 then you drive 55?

Does the trans down shift at half throttle or above maybe 3/4? Does the trans behave just like stock with regards to up-shift downshift? I have been thinking of this mod would complement an up powered motor. I have a isc in mine and just ordered a MP-8 so ill have to test it to see how the shifting and mileage change. The isc vs. isb in my RV have different rear end gear ratios so I'm sure that plays into TCM tuning. I like this subject but there isn't a lot of TCM tuners out there worth the money they charge. -DR

walt2137 · 11-10-2012, 03:56 PM

Well on our dynasty the Allison shifts to 6 gear at about 55 or 56 but I have seen my best mpg while traveling on a hwy with over 20 miles of construction at 45 and in 5 gear, what I do know is anything on our coach over 60 mph the mpg takes a serious nose dive.

deSanford · 11-10-2012, 04:28 PM

Ok guys this is what I'm doing and why. When my MH was first driven by me I couldn't get into 6th gear until I reached 62-67MPH. So I set my cruise control to 55 and speed-ed up to 62-67 MPH and when the trans shifted to 6th gear over drive I took my foot off the accelerator and let the speed drop down to the set speed of the cruise control (55). I noticed everything was good .......low boost, low pyro readings and cool temps on water and transmission fluid. Only one problem......when I encountered a small rise in the road the trans would down shift to 5th gear. Now I had to go through all the above to get back to 6th gear. In 5th gear overdrive the turbo boost and pyro temps along with of course the RPM would rise (higher water temps and trans oil temps). Now after I chipped (MP-8) the engine found more torque and HP. So with the new found torque and HP I figured out I need to have the trans TCM recalibrated. Now I go into 6th gear overdrive at 55 and I'm able to keep it there in "ECON" MODE and cruise control. If the grades are higher my trans will downshift to 5th and bring the speed back to 55MPH. If it can't it will downshift to 4th gear with higher revs which causes higher water and trans temps. When that happens I touch the cruise control and lower the speed 1MPH with each "touch". Trans appreciates that and I'm able to climb the hill in 5th gear overdrive or 6th gear. In "ECON" MODE I can go as low as 47MPH and still stay in 6th gear. No I have NOT changed any gearing in pumpkin or trans. When I'm in 6th gear overdrive etc everything is COOL and rpm is below 1500 at 55MPH. That is the speed I drive and my setup allows me to get the MOST MPG. Always working on making a good thing better I'm going with the Horton Fan clutch. For my ISB340 6.7L which by the way is the most fuel efficient Diesel Cummins makes in this class. The Horton model #9904013 made in Germany is a Viscous Directly Controlled Fan Drive. It is managed by the engine's electronic control module (ECM) for precision fan control. I believe when climbing hills I want the most cooling I can get therefore the old fan gets re installed. Again going up hills cool at less then 1500 RPM at 55MPH in 6th gear is the sweet spot for my setup at this time. When the present setup would drop automatically to 4th gear temps would rise. More cooling when needed is my idea of a cool setup. Also when cruising a low fan speed is cool. For those who have larger "L" engines they need more fuel to fill the area. I will also state I'm NO engine engineer just my common sense suggests my fuel theories. I have talked to lots of motorhome owners who have ISB engines and they for the most part all get over 10MPG. Your MPG might be different. Any questions? deSanford

DeadRinger · 11-10-2012, 04:58 PM

close enough thanks for the shift points

Barlow46 · 11-10-2012, 05:00 PM

Just one...it has been my experience that an engine/transmission downshift with increased rpm's when going up hills does not cause a rise in water temps or transmission temps. It usually results in lower temps. Higher rpms usually increase the flow of water through the cooling systems due to the water pump moving more water and providing more cooling for the engine/transmission. You seem to be saying that your temps increase with a downshift and increased rpm's and decrease as you induce a 5th gear upshift with lower rpm's when going up a hill. I am missing something somewhere in this explanation so educating me would be appreciated.

deSanford · 11-10-2012, 05:07 PM

With my set up the temps rise with higher RPM due to more friction of pistons going faster. Therefore my temps rise according to all my temperature indicators. My cooling system may not be sufficient for higher RPMs with the added torque and HP when climbing steep grades at 55MPH. Larger engines have larger cooling systems. I'm doing what I can to optimize my ride. deSanford PS with higher RPMs my turbo boost goes up along with the manifold temps etc.

Dutch Star Don · 11-10-2012, 06:03 PM

Okay.....It makes sense, as long as your not lugging that engine. I don't know what rpm range your engine is designed to run at vs mine.

I would expect for you to see all the way to 11 or 11.5 mpg depending on the terrain or distance of the trip. On flat terrain and longer trips, I get some pretty good fuel mileage. We drive at 58-59. Some just don't believe that anything faster than 59 -60 really starts to suck fuel exponentially.

We would really like to buy a newer coach, but I'm having a hard time justifying it. My perfect coach would be an 09 Dynasty 39' with the ISM, but the fuel hit would be huge. A local dealer has a similar coach in an 06 Beaver Patriot Thunder 39' with just 16000 miles. Unfortuneatly, it has the Cat 525 which I understand is a real fuel hog. Often, people say that if you can afford the coach you can afford the fuel. In this day and age, I don't beleive that is true in a lot of situations.